feat(db): add gacha-point balance + received tables

SVSim.Database/Models/ViewerGachaPointBalance.cs

@@ -0,0 +1,17 @@
+using Microsoft.EntityFrameworkCore;
+
+namespace SVSim.Database.Models;
+
+/// <summary>
+/// Per-viewer, per-pack gacha-point balance. Owned collection on <see cref="Viewer"/>.
+/// <c>PackId</c> = parent_gacha_id. <c>Points</c> accumulates one per pack opened (or
+/// <c>PackChildGachaEntry.OverrideIncreaseGachaPoint</c> when set on the child) and is
+/// decremented by <see cref="PackGachaPointConfig.ExchangeablePoint"/> per exchange.
+/// Unique index on (ViewerId, PackId) per feedback_owned_collection_unique_index.
+/// </summary>
+[Owned]
+public class ViewerGachaPointBalance
+{
+    public int PackId { get; set; }
+    public int Points { get; set; }
+}